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Occurrence and Ecological Impacts of Microplastics in Soil Systems: A Review


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Microplastics, as a group of emerging contaminants, are receiving growing attention. During the last decade, their occurrence and toxicity in aquatic ecosystems have been intensively studied and reviewed, but less attention has been paid on soil ecosystems. Given the importance of soil ecosystems and the call for increasing research on soil from scientific communities, it is predicted that relevant studies will boom in the following years. The present review intends to provide a comprehensive overview of current knowledge on microplastic pollution in soil environments. We critically summarize the source, contamination level and fate of microplastics in (industrial and arable) soils. Then, we thoroughly describe what effects have been observed on soil microbes, animals and plants, and analyze what insights we can get from available information. Finally, we identify knowledge gaps that need to be filled and give suggestions for future research.
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Bulletin of Environmental Contamination and Toxicology
Occurrence andEcological Impacts ofMicroplastics inSoil Systems:
FengxiaoZhu1· ChangyinZhu1· ChaoWang1· ChengGu1
Received: 15 January 2019 / Accepted: 22 April 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Microplastics, as a group of emerging contaminants, are receiving growing attention. During the last decade, their occur-
rence and toxicity in aquatic ecosystems have been intensively studied and reviewed, but less attention has been paid on soil
ecosystems. Given the importance of soil ecosystems and the call for increasing research on soil from scientific communities,
it is predicted that relevant studies will boom in the following years. The present review intends to provide a comprehensive
overview of current knowledge on microplastic pollution in soil environments. We critically summarize the source, contami-
nation level and fate of microplastics in (industrial and arable) soils. Then, we thoroughly describe what effects have been
observed on soil microbes, animals and plants, and analyze what insights we can get from available information. Finally, we
identify knowledge gaps that need to be filled and give suggestions for future research.
Keywords Microplastic· Distribution· Impact· Soil· Biota
Microplastics are generally defined as plastic parti-
cles < 5mm (Rillig etal. 2017). They have attracted increas-
ing concerns worldwide over the last decade, and extensive
studies have been conducted on their occurrence and impacts
in aquatic environments. Typical microplastics encountered
are shown in Fig.1.
Recent studies based on aquatic species have shown that
microplastics could be ingested/accumulated by aquatic
animals and cause detrimental effects on their survival and
health (Auta etal. 2017; Frydkjær etal. 2017). Given the
central role of soil in maintaining biodiversity, mediat-
ing nutrient cycling and providing food, it is imperative to
figure out how microplastics affect our terrestrial environ-
ments (especially soil environments), which has been largely
neglected during the past years. It was reported that soils are
probably receiving much more plastic wastes than the oceans
(Horton etal. 2017). Therefore, research is greatly needed
to focus on the problem of microplastic pollution in soil.
Indeed some recent studies (mostly published in
2016–2019) have begun to investigate the contamination
level and possible sources of microplastics in soil, as well
as their effects on the fitness of soil organisms (Huerta
Lwanga etal. 2016; Rodriguez-Seijo etal. 2017; Zhang and
Liu 2018). The results from these studies tend to confirm
that microplastics are ubiquitous and persistent contaminants
in soil as they were observed in the ocean (Zhang and Liu
2018), and that microplastics can affect the survival, growth,
reproduction, feeding and immune system of soil organisms
(Huerta Lwanga etal. 2016; Zhu etal. 2018a).
Therefore, the aim of this review is to provide an over-
view of current knowledge on the occurrence and likely eco-
logical impacts of microplastics in soil systems, and then to
outline the possible future research directions.
Microplastic pollution insoil systems
Microplastics can enter soil environments via multi-
ple routes, which has recently been reviewed by Bläsing
and Amelung (2018). In this paper, we are giving a con-
cise but comprehensive description, with new evidences
* Cheng Gu
1 State Key Laboratory ofPollution Control andResource
Reuse, School oftheEnvironment, Nanjing University,
Nanjing210023, China
Bulletin of Environmental Contamination and Toxicology
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(1) Land application of sludge and organic fertilizer may
introduce microplastics into soils. Previous studies
show that up to 90% of the microplastics from the
influent wastewater would be retained and accumu-
lated in the sludge, and the concentrations of micro-
plastics in sludge range from 1500 to 56,400 particles
kg−1 (Li etal. 2018; Mintenig etal. 2017). The pres-
ence of microplastics in organic fertilizers (up to 895
particles kg−1) has also been documented (Weithmann
etal. 2018). Hence, long-term application of sludge
and organic fertilizers may lead to soil pollution with
microplastics, which is evidenced by some previous
studies (Zubris and Richards 2005; Zhang and Liu
(2) Agricultural plastic film is another source for micro-
plastic pollution in soil. Plastic mulching has become
a widely used agricultural practice in many countries
for its instant economic benefits (Steinmetz etal. 2016).
For example, in 2015, mulch film consumption reached
1.455 million tons in China (Luo etal. 2018). The prob-
lem is that, it is not technically feasible to remove or
recycle most of the mulch films from the field because
they are usually very thin (0.01–0.03mm). Films
remaining in the field can slowly fragment into smaller
particles by a combination of physical, chemical and
biological effects (Barnes etal. 2009; Briassoulis etal.
2015), resulting in microplastic pollution.
(3) Atmospheric deposition may also serve as a significant
source of microplastics entering the surface soil. The
atmospheric fallout of microplastics in the urban areas
of Paris was estimated to be 2–355 particles m−2days−1
(Dris etal. 2016). In addition, detection of microplas-
tics in soils from remote unsettled high mountain areas
(Scheurer and Bigalke 2018), suggests that air deposi-
tion can be the major source in some areas.
(4) Other sources, such as wastewater irrigation, littering,
and surface runoff, may also be contributors to soil
microplastic pollution (Bläsing and Amelung 2018).
Overall, agricultural soils may receive microplastics
mainly from sludge/compost fertilization, plastic mulching
and wastewater irrigation. Whereas, air deposition might be
an important source for forest, urban and industrial soils
where regular fertilization and irrigation is not necessary.
However, since microplastic concentrations in fertilizer/
water/air can be highly variable and source studies are at an
early stage, the exact role of presumably important sources
for soils of different land uses is still unclear.
Fig. 1 Typical microplastics encountered in aquatic (and terrestrial)
environments. Polymer type refers to (Andrady 2011; Avio et al.
2017; Scheurer and Bigalke 2018); polymer structure refers to (Ency-
clopædia Britannica 2019); polymer density refers to (Andrady 2011;
Hidalgo-Ruz etal. 2012); microplastic morphotype refers to (Tanaka
and Takada 2016)
Bulletin of Environmental Contamination and Toxicology
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Numerous studies have been taken to investigate the distri-
bution of microplastics in marine environments (Auta etal.
2017), but information on the status of microplastic pol-
lution in soil environments is still quite limited. Here, we
provide a summary on relevant studies published recently.
Available data suggest that some industrial areas may
have been heavily contaminated with microplastics. For
instance, Fuller and Gautam (2016) found that soils near an
industrial area in Australia contained 0.03–6.7% of micro-
plastics (mainly PVC). On the other hand, results from
Scheurer and Bigalke (2018) demonstrated that microplastic
pollution in floodplain soils in Switzerland, although ubiqui-
tous, was less severe ( 0.00555% and 593 particles kg–1,
mainly PE).
Soil microplastic pollution in China deserves special
attention, since large amounts of plastics are produced,
consumed and discharged in China every year (Gourmelon
2015). Now, a few reports are available on the occurrence
of microplastic pollution in soils (mainly farmland soils)
in China. Results from these studies can be summarized as
follows: (1) In most soil samples, microplastic contents are
low ( ≤ 320 particles kg−1) (Lv etal. 2018; Liu etal. 2018;
Zhang etal. 2018); however, in soils with a history of sew-
age sludge amendment and wastewater irrigation, the con-
tent can be high ( > 7000 particles kg−1) (Zhang and Liu
2018), being higher than the general contents observed in
subtidal zones of the ocean (15–3320 particles kg−1) (Xu
etal. 2018). (2) Small size microplastics ( < 1mm) and fib-
ers are the most abundant ones (Lv etal. 2019; Zhang and
Liu 2018). (3) The main types of microplastics detected are
PE and PP (Lv etal. 2019; Liu etal. 2018). Here, it should
be mentioned that methods used for microplastic extraction
may influence the types of polymers recovered (see notes of
Table1). (4) Microplastics are present not only in top soils
(0–10cm) but also in deep soils (10–30cm). Top soils may
contain higher or lower concentrations of microplastics than
deep soils, which is dependent on the ease of the plastics to
penetrate into deep soil or to escape due to surface runoff
(Zhang etal. 2018).
Given that high microplastic content has been docu-
mented for some industrial, farmland and even forest soils
(Table1), to avoid soil quality deterioration, it is urgent to
conduct large scale and continuous surveys of microplastic
pollution in soils under different land uses. Information on
hotspot zones, major microplastics presented and associated
sources is essential for risk assessment and pollution con-
trol. In addition, to make different studies more comparable,
standardization of the units of measurement is required (Ng
etal. 2018). In a previous study, weight-based data pres-
entation was recommended for soil and sediment pollution
(Zhang etal. 2019). When assessing the contamination level
varying with time, weight-based microplastic content can
also be useful since introduction of new microplastics and
fragmentation of existing microplastics can be distinguished
in this way.
Degradation andtransport
Under natural conditions, microplastics are degraded due
to UV-radiation, thermal oxidation, physical abrasion and
biodegradation effects; during these processes, microplas-
tics undergo changes in polymer chemical structure, such as
chain cleavage, disproportionation, increase in oxygen-con-
taining functional groups, etc. (Luo etal. 2018). But these
processes are very slow (especially in soil) because (micro)
plastics are recalcitrant in nature. Earlier studies showed that
PP degradation in soil was minimal (0.4%) after one year
(Arkatkar etal. 2009) while no degradation was observed
for PVC and PS buried under soil for over 32years (Otake
etal. 1995).
Although optimal conditions may not be met in real envi-
ronments, biodegradation is still one of the most promising
ways to reduce microplastic pollution in the environment
(Auta etal. 2017). Some efforts have been made by exploit-
ing the potentials of terrestrial organisms. Notably, wax-
worms and mealworms are reported to be able to efficiently
digest PE or PS plastics (Brandon etal. 2018; Yang etal.
2015a). Moreover, a range of bacterial and fungal strains
capable of degrading (micro) plastics have been isolated
from the environment or animal guts (Ali etal. 2014; Krue-
ger etal. 2015; Yang etal. 2015b).
Like other pollutants, microplastics in soil can move.
They can travel short distances through bioturbation and
agricultural practices (such as ploughing). Bioturbation-
related microplastic movement receives more interests,
and some earthworm (Rillig etal. 2017) and collembolan
(Maaß etal. 2017) species are found to transport micro-
plastic particles from surface soil to deep soil. In addi-
tion, there are also evidences showing that microplastics
can travel long distances through surface runoff and soil
erosion, by which they can enter water bodies and even
the ocean (Nizzetto etal. 2016). Furthermore, the co-
transport of organic/inorganic pollutants and microplas-
tics (which act as an active adsorbent) may have essential
environmental consequences, which has drawn consider-
able attention in both aquatic and terrestrial ecosystems
(Browne etal. 2013; Wijesekara etal. 2018; Yang etal.
Bulletin of Environmental Contamination and Toxicology
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Table 1 Available data on the status of microplastic pollution in soil
Notes: (1) /—relevant information is not available. (2) shallow—shallow soil (0–3 cm); deep1—deep soil (3–6cm); top—top soil (0–10cm); deep—deep soil (10–30 cm). (3) a—data are the total
number of total mesoplastic and microplastic particles detected but microplastics accounts for more than 95%; b—The methods used for microplastic extraction in that study may significantly
underestimate the abundance of dense polymers such as PVC and PET. (4) GC–MS stands for gas chromatography-mass spectrometer; FT-IR stands for Fourier transform-infrared spectroscopy
Country Soil source Microplastics Methods for microplastic extraction,
identification and quantification
Concentration Major size
Major type Morphotype
(%) (particles kg−1)
Australia Near the industrial area 0.03–6.7 / / PVC / Pressurized fluid extraction GC–MS
and FT-IR spectrophotometer analysis
Fuller and Gautam (2016)
Switzerland Floodplain soils ≤ 0.0055 ≤ 593 < 0.5 PE / Density separation using 27% NaCl
solution 65% HNO3 treatment of
organic matter FT-IR microscope
Scheurer and Bigalke (2018) b
China (Shanghai) Rice-fish co-culture ecosys-
/10.3 ± 2.2 < 1 PE, PP Mainly fibers Density separation using saturated NaCl
solutions 30% H2O2 treatment of
organic matter Identification under
the microscope
Lv etal. (2019) b
China (Shanghai) Vegetable fields / 78.0 ± 12.9 shallow
62.5 ± 13.0 deep1
< 1 PE, PP Fibers and fragments Density separation with saturated NaCl
solution 30% H2O2 treatment of
organic matter µ-FT-IR assay
Liu etal. (2018) b
China (Northwest
Agricultural field ≤ 0.000054 40 ± 126 top
100 ± 141 deep
> 0.1 Low density micro-
plastics (such as
PE and PP) were
/ Water floatation method heat treat-
ment of microplastics at 130°C for
3–5s Identification under the
microscope before and after heat
Zhang etal. (2018) b
Greenhouse field 100 ± 254 top
80 ± 193 deep
Fruit field 320 ± 329 top
120 ± 129 deep
China (Southwest
Greenhouse vegetable soils / 7100–42,960a < 1 / Mainly fibers Density separation using saturated NaI
solution H2O2 treatment of organic
matter method)
Zhang and Liu (2018)
Forest buffer zone / 8180–18,100a < 1 / Mainly fibers
Bulletin of Environmental Contamination and Toxicology
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Ecological impacts ofmicroplastics onsoil
How domicroplastics aect soil microorganisms?
The interaction of microplastics with soil microbiota
remains largely unexplored. Only a few studies have inves-
tigated the effects of microplastics in soil systems, mainly
on overall microbial activity, bacterial transport, and spread
of antibiotic resistant genes (ARGs).
PP particles (7% and 28%) were reported to have a posi-
tive effect on soil microbial activity (Liu etal. 2017), while
polyacrylic (0.05–0.4%), polyester (0.05–0.4%) and PS par-
ticles (1mgkg−1) showed a negative effect (Awet etal. 2018;
de Souza Machado etal. 2018). Since polymer type, shape,
size and concentration varied in these studies, it is difficult
to draw a general conclusion on the toxicity of microplastics
based on their features. Modified soil structure and microbial
community composition have been proposed to be the pos-
sible reasons for altered microbial activity in these studies,
however no direct evidences/linkages have been provided or
observed. Further investigations are needed to improve our
understanding of the effects and mechanisms of microplas-
tics on soil microbial metabolism and activity.
The effect of microplastics on the transport and deposi-
tion of soil microorganisms has not been intensely exam-
ined, but some insights may be gained from the study by He
etal. (2018). The authors found that under low ionic strength
conditions PS particles had negligible effect on Escherichia
coli transport in quartz sand, whereas under high ionic
strength conditions, plastic particles stimulated bacterial
transport. They proposed that the adsorption of plastic par-
ticles onto cell surfaces and the repel effect were the main
driver for the increased cell transport induced by plastics
at nanoscale (20nm), while plastics at microscale (2μm)
mainly increased cell transport by competing for deposition
sites on sand. Further research is needed to investigate how
microplastics affect microbial movement in real soil systems.
Spread of ARGs is an increasing concern, due to its
potential adverse effects on human health. Studies based
on aquatic ecosystems reveal that microplastics can serve
as hotspots of gene exchange between phylogenetically dif-
ferent microorganisms by introducing additional surface,
thus having a potential to increase the spread of ARGs and
antibiotic resistant pathogens in water and sediments (Arias-
Andres etal. 2018; Huang etal. 2019; Imran etal. 2019). In
soil ecosystems, the presence of PS microplastics (0.1%) has
been shown to increase the retention time of antibiotics and
ARGs (Sun etal. 2018). More evidences are needed to draw
a conclusion on whether microplastic pollution facilitates
the transmission of ARGs in soil environments.
How domicroplastics aect soil animals?
Knowledge about the impacts of microplastics on the health
of soil animals lags far behind that of aquatic animals. Only
a few soil invertebrates have been examined, including
nematodes, oligochaeta (e.g. earthworms), collembolan
and isopods. Microplastics were either added in liquid
medium, food or soil matrix in previous studies, to study
their effect on the survival, growth, reproduction, inflamma-
tory response, metabolic activity, feeding behavior, neurode-
generation and gut microbiota of soil animals.
When assessing the toxicological effect of microplas-
tics on nematodes, size is an important factor to be con-
sidered (Lei etal. 2018; Kim etal. 2019). Lei etal. (2018)
chronically exposed Caenorhabditis elegans to 1mg L−1
PS particles (0.1, 0.5, 1.0, 2.0 and 5.0µm) for 3days. They
found that the 1.0μm group had the lowest survival rate, the
shortest average lifespan and the largest decrease in body
length; 1.0μm particles also significantly downregulated the
expression of unc-17 and unc-47 genes, reflecting damages
to cholinergic and GABAergic neurons in nematodes. The
strongest toxicity of 1.0μm PS particles might be due to
that the moderate-sized plastic particles were more readily
taken by nematodes; this hypothesis was supported by the
observation that 1.0μm particles showed higher accumula-
tion than others.
Studies on oligochaeta show that the effect of micro-
plastics is highly dependent on the level of exposure. For
instance, Zhu et al. (2018a) reported a concentration-
dependent effect of PS nanoplastics on the weight of the
soil oligochaete Enchytraeus crypticus: 0.025% (in oatmeal)
having a slightly positive effect; 0.5% having no effect; 10%
having a significantly negative effect; in addition, a clear
shift in the gut microbiota was only observed under the
highest exposure (10%). These findings are in line with the
results from Huerta Lwanga etal. (2016) that 7% PE micro-
plastics in plant litter (corresponding to 0.2% in soil) had no
effect on the growth and survival of the earthworm Lumbri-
cus terrestris but 28–60% addition had an inhibitory effect.
Previous studies also suggest that histological analysis
may be used for early diagnoses when assessing the tox-
icity of microplastics on oligochaeta in soil, and that bio-
degradable plastics are not intrinsically less toxic than
conventional plastics. For instance, Rodriguez-Seijo etal.
(2017) reported that, although addition of low density PE
microplastics (0.0625–1% in soil) showed no effect on the
survival and growth of the earthworm Eisenia Andrei, tissue
damage and immune system responses were observed even
under the lowest exposure level. Qi etal. (2018) reported
that, when applied at the same dosage (1% in soil), micro-
plastics derived from starch-based biodegradable films had
more effects on earthworm growth than conventional low
Bulletin of Environmental Contamination and Toxicology
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density PE films. This was possibly because the biodegrad-
able plastics were mainly composed of PET and polybutyl-
ene terephthalate, which might be more toxic than PE.
Soil collembolan species seem to be sensitive to micro-
plastic pollution. Zhu etal. (2018b) reported that exposure to
0.1% PVC microplastics for 56days, significantly inhibited
the growth (by 16.8%) and reproduction (by 28.8%) of Folso-
mia candida in soil, and significantly modified the metabolic
turnover of this animal (as indicated by changes in δ15N and
δ13C values). Recently, Ju etal. (2019) reported a similar neg-
ative effect of PE microplastic exposure (0.1–1%) on Folso-
mia reproduction. In both studies, altered animal gut bacterial
community due to microplastic exposure were also observed.
These results suggest that collembolan may be used as a valu-
able bioindicator of microplastic disturbance in soil.
Isopods are commonly used as test species in ecotoxicity
studies, due to their important role in plant litter decomposi-
tion processes (Drobne 1997) Kokalj etal. (2018). assessed
the effects of PE microplastics presented in food pellets
(0.4%) on the feeding behavior and energy reserve of iso-
pods. After 14days exposure, no effects on any end-point
(including food ingestion rate, defecation rate, food assimi-
lation rate and efficiency, body mass change, mortality and
energy reserves in the digestive glands) were observed, sug-
gesting little hazardous effects of PE microplastics to the iso-
pod Porcellio scaber. Further work is needed to investigate
the potential longer-term effects of such exposure, as well as
the effects of other commonly detected microplastics in soil.
How domicroplastics aect plants?
When it comes to plants, people are concerned about two
questions: whether plant can absorb and accumulate micro-
plastics, and how microplastics affect plant growth and
food quality. Currently, such information is scarce, possibly
because it is difficult to identify microplastics in plant tissues
and the effect on crops has not attracted enough attention.
It is likely that small-sized microplastics can overcome
cell wall and membrane barriers. The possibility of plant
uptake of microplastics can be investigated with the aid of
fluorescent microbeads. For example, a cell culture-based
study demonstrated that nano-scale ( < 100nm) fluorescent
PS beads could enter tobacco cells through endocytosis
(Bandmann etal. 2012). More importantly, a recent study
based on whole plant cultures showed that edible plant could
uptake and accumulate micro-scale (0.2μm) fluorescent PS
beads from soil (Li etal. 2019), highlighting the potential
risks of microplastic uptake by humans via food web chain.
Currently, only one study has been carried out to inves-
tigate the impacts of microplastics on plants. By adding
1% biodegradable and PE plastic particles in soil, Qi etal.
(2018) found that both types of microplastics disturbed the
growth of wheat, with the former having a stronger negative
effects than the latter. Fruit biomass was also negatively
affected by biodegradable plastic particles. Interestingly, the
presence of earthworm alleviated the impairments in wheat
induced by microplastics. In this study, the accumulation of
PE particles in plant tissue was not examined.
The role ofmicroplastic‑associated organic
orinorganic pollutants inmicroplasticinduced
It is noted that in previous studies, microplastics are often
considered as pure polymers or pure physical particles.
In fact, microplastics may contain substantial amounts of
chemical additives added intentionally (such as plasticiz-
ers and flame retardants) or toxic pollutants adsorbed from
the surrounding environment (such as polycyclic aromatic
hydrocarbons and heavy metals) (Hong etal. 2017), which
could be a real hazard to soil organisms. At present, the
role of these organic or inorganic pollutants in microplas-
tic-induced stresses has drawn little attention, although the
possibility of pollutant transfer from soil microplastics to
earthworms has been demonstrated (Gaylor etal. 2013). In
other ecosystems, microplastic-associated pollutants have
been shown to play a vital role in determining the toxicity of
microplastics to marine animals (Browne etal. 2013; Olivi-
ero etal. 2019) or sludge digestive microbiota (Wei etal.
2019). It suggests that pollutants associated with environ-
mental microplastics should be considered in further toxi-
cological studies. Particular attention should be paid to the
pollutants that are highly toxic or at high concentrations, as
not all pollutants are sufficient to cause a significant negative
effect (Zhang etal. 2019).
Knowledge gap andfuture recommendations
Based on this review, we can see that although our under-
standing of microplastics in soil environments is advancing,
there is still a remarkable lack of relevant data. For example,
the characteristics of microplastic pollution in soil environ-
ments, their potential ecological effects and the underpin-
ning mechanisms of their toxicity are far from fully under-
stood. Therefore, in future studies, the most important issues
needed to be addressed are as follows:
(1) Firstly, we need to understand the distribution of
microplastics in soil ecosystems, and answer basic
questions like: What is the extent of microplastic
pollution in soils of different land uses? What are
the major sources? Which microplastics (in terms of
polymer type, shape and size) are the most abundant
ones? Although current literatures suggest PE and PP
polymers, small size ( < 1mm) particles, and fibers are
generally more abundant than their counterparts, more
Bulletin of Environmental Contamination and Toxicology
1 3
evidences are needed to confirm whether it is true since
methods used in most previous studies have underesti-
mated the abundance of dense particles (such as PVC
and PET). In addition, considering that additives and
environmental contaminants associated with micro-
plastics may have a profound effect on the toxicity of
microplastics, it is better to include information on the
concentration of these compounds in future surveys.
(2) Then, we need to understand their ecological effects
and associated controlling factors, so that we can
answer critical questions like: How do microplastics
affect the mobility, abundance, diversity, composition
and function of soil organisms? Would an effect be
observed at environmentally relevant concentrations?
How do microplastic features and soil type influence
the ecological effects of microplastics? This informa-
tion is the basis for a precise risk assessment.
(3) Meanwhile, we need to get a better understanding about
the mechanisms of the ecological effects observed. For
instance, are microplastics mainly acting as a physical
or chemical hazard? Currently little has been done to
clarify the contribution of chemical (degradation prod-
ucts, polymer additives or environmental chemicals
adsorbed on the surface) release from microplastics
to their toxicity in the context of soil; the molecular
mechanisms of microplastic-induced ecotoxicity are
also unclear. We believe that they are among the most
important questions remaining to be answered in this
Acknowledgements This work was financially supported by National
Key Research and Development Plans (2018YFC1800602) and the
National Science Foundation of China (21777066).
Compliance with Ethical Standards
Conflict of interest The authors declare that there is no conflict of in-
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... MP pollution has been regarded as a global emerging issue in agricultural ecosystems (Zhu et al. 2019). An investigation in the vegetable farmlands of suburb Wuhan, China indicated that the abundance of MPs ranged from 320 to 12,560 n·kg −1 (Chen et al. 2020). ...
... A survey showed that approximately 90% of MPs in the sewage would accumulate in the sludge of a treatment plant (Mahon et al. 2017). The treated sludge is used as fertilizer, resulting in the accumulation of MPs in soils (Zhu et al. 2019). Moreover, irrigation and infiltration of surface water lead to a large increase in MPs in soils (Zhou et al. 2020). ...
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Microplastics (MPs) have become a hot issue of environmental pollution. However, insufficient evidence exists regarding the distributions and fates of MPs in terrestrial environment, especially in farmlands. The distributions of MPs in paddy fields were investigated in Xiangtan City, a typical rice production area in China. The abundance of MPs in paddy seedling raising fields was 3805 ± 511 n·kg⁻¹, which increased by approximately 9 times than that in common paddy fields. Transparent films became the dominant forms due to the huge usage of mulching films, corresponding to that the proportion of polyvinyl chloride (PVC) increased to 17% there. Moreover, an industrial plant nearby also contributed considerably to the MP pollution; the proportion of PVC (33%) in the paddy fields nearby increased to approximately 4 times of common paddy fields, while polyvinyl alcohol (PVA; 13%) used as an important chemical raw material to synthesis in various applications was uniquely detected there. These results highlight the input of MPs from agricultural and industrial activities in farmlands. Their contributions to the MP pollution in farmlands should be continuously investigated.
... Previous reviews gave an extensive overview of potential occurrences of plastic debris in terrestrial systems Zhu et al., 2019;Dioses-Salinas et al., 2020;Wu et al., 2020a;Meixner et al., 2020) and reflected on the suitability of generic methods for soil plastic analysis (Bläsing and Amelung, 2018;Möller et al., 2020). Our review, in contrast, specifically aims at critically discussing and evaluating current sample preparation techniques for the microplastic analysis of soil. ...
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The use of agricultural plastic covers has become common practice for its agronomic benefits such as improving yields and crop quality, managing harvest times better, and increasing pesticide and water use efficiency. However, plastic covers are suspected of partially breaking down into smaller debris and thereby contributing to soil pollution with microplastics. A better understanding of the sources and fate of plastic debris in terrestrial systems has so far been hindered by the lack of adequate analytical techniques for the mass-based and polymer-selective quantification of plastic debris in soil. The aim of this dissertation was thus to assess, develop, and validate thermoanalytical methods for the mass-based quantification of relevant polymers in and around agricultural fields previously covered with fleeces, perforated foils, and plastic mulches. Thermogravimetry/mass spectrometry (TGA/MS) enabled direct plastic analyses of 50 mg of soil without any sample preparation. With polyethylene terephthalate (PET) as a preliminary model, the method limit of detection (LOD) was 0.7 g kg−1. But the missing chromatographic separation complicated the quantification of polymer mixtures. Therefore, a pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) method was developed that additionally exploited the selective solubility of polymers in specific solvents prior to analysis. By dissolving polyethylene (PE), polypropylene (PP), and polystyrene (PS) in a mixture of 1,2,4-trichlorobenzene and p-xylene after density separation, up to 50 g soil became amenable to routine plastic analysis. Method LODs were 0.7–3.3 mg kg−1, and the recovery of 20 mg kg−1 PE, PP, and PS from a reference loamy sand was 86–105%. In the reference silty clay, however, poor PS recoveries, potentially induced by the additional separation step, suggested a qualitative evaluation of PS. Yet, the new solvent-based Py-GC/MS method enabled a first exploratory screening of plastic-covered soil. It revealed PE, PP, and PS contents above LOD in six of eight fields (6% of all samples). In three fields, PE levels of 3–35 mg kg−1 were associated with the use of 40 μm thin perforated foils. By contrast, 50 μm PE films were not shown to induce plastic levels above LOD. PP and PS contents of 5–19 mg kg−1 were restricted to single observations in four fields and potentially originated from littering. The results suggest that the short-term use of thicker and more durable plastic covers should be preferred to limit plastic emissions and accumulation in soil. By providing mass-based information on the distribution of the three most common plastics in agricultural soil, this work may facilitate comparisons with modeling and effect data and thus contribute to a better risk assessment and regulation of plastics. However, the fate of plastic debris in the terrestrial environment remains incompletely understood and needs to be scrutinized in future, more systematic research. This should include the study of aging processes, the interaction of plastics with other organic and inorganic compounds, and the environmental impact of biodegradable plastics and nanoplastics.
... MPs can pollute the environment by adsorption of heavy metals, pesticides, dyes, and transporting the contaminants (Kumar et al. 2020). MPs can accumulate in plants, affect plant growth, and eventually enter the food chain (Zhu et al. 2019). MPs can affect microbial transport, metabolism activity, and genetic exchange. ...
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Fertilizers play an essential role in increasing crop yield, maintaining soil fertility, and provide a steady supply of nutrients for plant requirements. The excessive use of conventional fertilizers can cause environmental problems associated with nutrient loss through volatilization in the atmosphere, leaching to groundwater, surface run-off, and denitrification. To mitigate environmental issues and improve the longevity of fertilizer in soil, controlled release fertilizers (CRFs) have been developed. The application of CRFs can reduce the loss of nutrients, provide higher nutrient use efficiency, and improve soil health simultaneously to achieve the goals of climate-smart agricultural (CSA) practices. The major findings of this review paper are (1) CRFs can prevent direct exposure of fertilizer granule to soil and prevent loss of nutrients such as nitrate and nitrous oxide emissions; (2) CRFs are less affected by the change in environmental parameters, and that can increase longevity in soil compared to conventional fertilizers; and (3) CRFs can maintain required soil nitrogen levels, increase water retention, reduce GHG emissions, lead to optimum pH for plant growth, and increase soil organic matter content. This paper could give good insights into the ongoing development and future perspectives of CRFs for CSA practices. Graphical abstract
... On the contrary, other studies have confirmed the accumulation of MP in plant tissues, at least for those characterized by a very small size between 0.2 μm and 2 μm (Bandmann et al., 2012;Li et al., 2020c). Recently, Zhu et al. (2019) speculated that, due to their small size, MP could cross the cell wall barrier and then be acquired by roots. Interestingly, detected PS microbeads with different sizes in the edible part of lettuce (L. ...
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Microplastics (MP) are ubiquitous contaminants of great concern due to their high persistence and potential hazardous impact on the environment. Depending on their size and shape, as well as the chemical additives they can have in their polymeric structure, MP can be taken up by organisms, ultimately leading to direct and indirect toxic effects. In this review, we discuss the primary sources, fate, and impact of MP on the rhizosphere ecology, focusing in particular on how soil physical-chemical properties, plant physiology, and soil biodiversity are modulated by the interaction of MP in the plant-soil system. Current knowledge on soil ecotoxicology shows that MP directly affects soil quality and fertility via alteration of soil nutrient cycling and microbial communities and indirectly by changing soil bulk density, pH, porosity, electric conductivity, and nutrient bioavailability. MP is also known to affect soil animals by altering their feeding, mobility, and reproductive behavior. Toxic effects of MP on the multiple and co-occurring interactions among the soil, soil organisms and plants, particularly in the long-term, remain unstudied. Indeed, a better understanding of rhizosphere-MP interactions at a functional level (e.g., nutrient availability, pollutant immobilization, root exudates, etc.) is urgently needed to develop risk assessment frameworks of soil pollution by MP.
... While this has helped to promote food security in many countries worldwide, it has also left a widespread legacy of plastic pollution which threatens future food production and agroecosystem health (FAO, 2021;Liu et al., 2014). The main sources of plastics entering soil come from the use of plastic mulch films, sewage irrigation, sludge application and aerial deposition Zhu et al., 2019). Much of this contamination is present as macro-plastic, however, this progressively fragments into smaller particles through mechanical abrasion (e.g. ...
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Microplastic contamination in agroecosystems is becoming more prevalent due to the direct use of plastics in agriculture (e.g., mulch films) and via contamination of amendments (e.g., compost, biosolids application). Long-term use of agricultural plastics and microplastic pollution could lead to soil degradation and reduced crop health due to the slow degradation of conventional plastics creating legacy plastic. Biodegradable plastics are more commonly being used, both domestically and in agriculture, to minimise plastic pollution due to their biodegradable nature. However, the influence of a biodegradable plastics on soil function at the field scale is largely unknown. We investigated the effect of conventional (polyethylene) and biodegradable (PHBV) microplastics on N2O emissions and soil biochemical processes in a field trial of winter barley. Microplastic was added to the soil at realistic levels (100 kg ha⁻¹) for both conventional and biodegradable treatments. N2O emissions were measured throughout the growing season alongside key soil quality indicators (microbial community composition, ammonium, nitrate, moisture content, pH and EC). Overall, microplastic addition had no observable effect on crop yield, microbial communities or soil biochemical properties. Yet, we found cumulative N2O emissions were reduced by two-thirds following conventional microplastic addition compared to the no-plastic and biodegradable microplastic treatments. We believe this response is due to the lower soil moisture levels over the winter in the conventional microplastic treatment. Overall, the response of key soil parameters to microplastic addition show fewer negative effects to those seen in high dose laboratory mesocosm experiments. Thus, it is imperative that long-term field experiments at realistic dose rates be undertaken to quantify the real risk that microplastics pose to agroecosystem health.
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Owing to their wide distribution, easy production, and resistance to degradation, microplastics (MPs) represent a globally emerging group of pollutants of concern. Furthermore, their decomposition can result in the generation of nanoplastics (NPs), which cause further environmental issues. Currently, the impact of the combination of these plastics with other organic pollutants on crop growth remains poorly investigated. In this study, a hydroponic experiment was conducted for seven days to evaluate the effects of 50 nm, 50 mg/L polystyrene (PS), and 1 mg/L phenanthrene (Phe) on the growth of rice plants. The results revealed that both Phe and PS inhibited growth and improved the antioxidant potential of rice. Relative to Phe alone, exposure to a combination of PS and Phe reduced Phe accumulation in the roots and shoots by 67.73% and 36.84%, respectively, and decreased the pressure on the antioxidant system. Exposure to Phe alone destroyed the photosynthetic system of rice plant leaves, whereas a combination of PS and Phe alleviated this damage. Gene Ontology (GO) analysis of the rice transcriptomes revealed that detoxification genes and phenylalanine metabolism were suppressed under exposure to Phe, which consequently diminished the antioxidant capacity and polysaccharide synthesis in rice plants. Kyoto Encyclopaedia of Genes and Genomes (KEGG) transcriptome analysis revealed that the combined presence of both PS and Phe improved photosynthesis and energy metabolism and alleviated the toxic effects of Phe by altering the carbon fixation pathway and hormone signal transduction in rice plants. The combination of PS and Phe also prevented Phe-associated damage to rice growth. These findings improve our understanding of the effects of MP/NPs and polycyclic aromatic hydrocarbons on crops.
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The polystyrene micro-plastics (Ps-MPs) is one of the leading pollutants found in both aquatic and terrestrial ecosystems. While most of the studies on the morphology and cyto-toxicity of MPs have been based on aquatic organisms, their effects on terrestrial plants are still scarcely known. The present study was an attempt to measure the effect of different sizes (80, 100, 200, 500, 1000, 2000, 4000, and 8000 nm) and concentrations (100 and 400 mg/L) of Ps-MPs on the root length and chromosomes of root tip cells of Allium cepa using A. cepa root chromosomal aberration assay. Large size Ps-MPs (4000 and 8000 nm) showed the highest reduction in A. cepa root length; however, the differences were not significant (at p ≤ 0.05), with respect to negative control (Milli-Q water). The mitotic index showed both significant size- and concentration-dependent decreases, being the lowest (12.06%) in 100 nm at 100 mg/L concentration, with respect to the control (25.05%). The chromosomal abnormality index (CAI) and nuclear abnormality index (NAI) showed significant decreases, with respect to negative control. In addition, the induction of micro-nucleated cells was also observed in Allium root tip cells, when treated with MPs of all sizes, which can predict direct DNA damage to the plant cells. Hence, we conclude that most of the MP sizes caused cyto-toxic and nuclear damage by adversely impacting the spindle formation and induction of micro-nucleated cells in Allium cepa root tip cells. To the best of our knowledge, this is the first study that showed the effect of considerable size range of Ps-MP sizes on the root length and cell division in plants.
Microplastic (MP, 100 nm-5 mm) may present an attributable risk to ecosystem and human health, and its pollution has become a global environmental concern. Despite a wealth of information on the accumulation of MPs in aquatic species, there is no information on the uptake and accumulation of MPs by higher plants. Terrestrial edible plants are directly exposed to MPs when agricultural soil was applied with organic manure, sewage sludge as fertilizer or plastic mulching. In this paper, the uptake of two sizes of polystyrene (PS) microbeads (0.2 and 1.0 μm) and then their distribution and migration in an edible plant lettuce were firstly investigated based on laboratory experiments. We used fluorescent markers to track PS microbeads in plant tissues and found fluorescence to be a sensitive and reliable detection method. Sections from untreated control lettuce showed no autofluorescence. When roots were treated with fluorescently labeled PS microbeads, the microbeads could be identified by its fluorescence. Our main study investigated the uptake of 0.2 μm beads, as few luminescence signals were observed in lettuce roots for 1.0 μm beads in our experiment. We observed that 0.2 μm fluorescent microbeads were extracellularly trapped in the root cap mucilage (which is a highly hydrated polysaccharide) and a "dark green tip" (which was typical of lettuce roots exposed to label PS beads) was usually visible to the naked eye. Confocal images revealed that the PS luminescence signals were mainly located in the vascular system and on the cell walls of the cortex tissue of the roots, indicated that the beads passed through the intercellular space via the apoplastic transport system. Once inside the central cylinder, the 0.2 μm PS beads were transferred from the roots to the stems and leaves via the vascular system following the transpiration stream. We also observed that the PS beads adhered to one another and self-assembled systematically into "grape-like" and "(chain) string-like" clusters in the intercellular space of the root and stem vascular tissue of lettuce plant. In contrast to the root and stem, PS beads were dispersed in the leaf tissue. Here, for the first time we provide evidence of the adherence, uptake, accumulation, and translocation of submicrometer MPs within an edible plant. Our findings highlight the previously underappreciated human exposure pathway to MPs through the consumption of contaminated crops and emphasize the need for new management strategies to control the release of MPs waste products into the terrestrial environment. Ultimately, the potential impacts of low range sized MPs on food safety of crop plants and human health need to be urgently considered.
Microplastics and antibiotic resistance genes (ARGs) are emerging pollutants/contaminants, and are also the research hotspots concerning environmental health in the past few years. To explore the effects of microplastics on ARGs in estuarine sediment, three different microplastics were added to microcosm incubation experiments of sediments. Then, we investigated the persistence, abundance, diversity, and shifts of the ARGs in estuarine sediments by high-throughput quantitative polymerase chain reaction (PCR). The results showed that the microplastics significantly changed the structure of ARGs in the sediments. PVC and PE, which are hard to degrade, had significant effects on the structures and types of ARGs. However, the PVA, which is soluble, reduced the types and persistence of ARGs significantly. The abundance of ARGs in S_PVC, S_PE, and S_PVA were 4.1×109, 8.1×109, and 2.0×109 copies·g-1, respectively. The abundance of ARGs in sediments with added PE almost increased by one order of magnitude, implying that microplastics could significantly increase the abundance of ARGs in sediments. Furthermore, OLS regression analysis showed that ARGs are significantly correlated with transposon and integron, suggesting that mobile genetic elements (MGEs) may promote the transfer and dissemination of ARGs.
The retention of polyvinyl chloride (PVC) microplastics in sewage sludge during wastewater treatment raises concerns. However, the effects of PVC microplastics on methane production from anaerobic digestion of waste activated sludge (WAS) have never been documented. In this work, the effects of PVC microplastics (1 mm, 10-60 particles/g TS) on anaerobic methane production from WAS were investigated. The presence of 10 particles/g TS of PVC microplastics significantly ( P = 0.041) increased methane production by 5.9 ± 0.1%, but higher levels of PVC microplastics (i.e., 20, 40, and 60 particles/g TS) inhibited methane production to 90.6 ± 0.3%, 80.5 ± 0.1%, and 75.8 ± 0.2% of the control, respectively. Model-based analysis indicated that PVC microplastics at >20 particles/g TS decreased both methane potential (B0) and hydrolysis coefficient (k) of WAS. The mechanistic studies showed that bisphenol A (BPA) leaching from PVC microplastics was the primary reason for the decreased methane production, causing significant ( P = 0.037, 0.01, 0.004) inhibitory effects on the hydrolysis-acidification process. The long-term effects of PVC microplastics revealed that the microbial community was shifted in the direction against hydrolysis-acidification and methanation. In conclusion, PVC microplastic caused negative effects on WAS anaerobic digestion through leaching the toxic BPA.
Microplastics are defined as plastic fragments <5 mm, and they are found in the ocean where they can impact on the ecosystem. Once released in seawater, microplastics can be internalized by organisms due to their small size, moreover they can also leach out several additives used in plastic manufacturing, such as plasticizers, flame retardants, etc., resulting toxic for biota. The aim of this study was to test the toxicity of micronized PVC products with three different colors, upon Paracentrotus lividus embryos. In particular, we assessed the effects of micronized plastics and microplastic leachates. Results showed a decrease of larval length in plutei exposed to low concentrations of micronized plastics, and a block of larval development in sea urchin embryos exposed to the highest dose. Virgin PVC polymer did not result toxic on P. lividus embryos, while an evident toxic effect due to leached substances in the medium was observed. In particular, the exposure to leachates induced a development arrest immediately after fertilization or morphological alterations in plutei. Finally, PVC products with different colors showed different toxicity, probably due to a different content and/or combination of heavy metals present in coloring agents.
Microplastics (MPs) are an emerging contaminant and are confirmed to be ubiquitous in the environment. Adverse effects of MPs on aquatic organisms have been widely studied, whereas little research has focused on soil invertebrates. We exposed the soil springtail Folsomia candida to artificial soils contaminated with polyethylene MPs (<500 μm) for 28 d to explore the effects of MPs on avoidance, reproduction, and gut microbiota. Springtails exhibited avoidance behaviors at 0.5% and 1% MPs (w/w in dry soil), and the avoidance rate was 59% and 69%, respectively. Reproduction was inhibited when the concentration of MPs reached 0.1% and was reduced by 70.2% at the highest concentration of 1% MPs compared to control. The half-maximal effective concentration (EC50) value based on reproduction for F. candida was 0.29% MPs. At concentrations of 0.5% dry weight in the soil, MPs significantly altered the microbial community and decreased bacterial diversity in the springtail gut. Specifically, the relative abundance of Wolbachia significantly decreased while the relative abundance of Bradyrhizobiaceae, Ensifer and Stenotrophomonas significantly increased. Our results demonstrated that MPs exerted a significant toxic effect on springtails and can change their gut microbial community. This can provide useful information for risk assessment of MPs in terrestrial ecosystems.
Nanoplastics are widely used in modern life, for example, in cosmetics and daily use products, and are attracting concern due to their potential toxic effects on environments. In this study, the uptake of nanopolystyrene particles by Caenorhabditis elegans (C. elegans) and their toxic effects were evaluated. Nanopolystyrene particles with sizes of 50 and 200 nm were prepared, and the L4 stage of C. elegans was exposed to these particles for 24 h. Their uptake was monitored by confocal microscopy, and various phenotypic alterations of the exposed nematode such as locomotion, reproduction and oxidative stress were measured. In addition, a metabolomics study was performed to determine the significantly affected metabolites in the exposed C. elegans group. Exposure to nanopolystyrene particles caused the perturbation of metabolites related to energy metabolism, such as TCA cycle intermediates, glucose and lactic acid. Nanopolystyrene also resulted in toxic effect including induction of oxidative stress and reduction of locomotion and reproduction. Collectively, these findings provide new insights into the toxic effects of nanopolystyrene particles.
Microplastics (MP) (<5 mm) are crucial pollution which are widely distributes in the environment. Recently, the studies of MP have increased rapidly due to increasing awareness of the potential and growing risks of biological effects during storage and disposal. However, due to limitations in analytical methods and the methods of environmental risk assessment, the distribution and biological effects of MP are still debatable issues. To clarify the potentially environmental and biological impacts of MP in the consecutive environment, (1) analytical methods to assess MP, (2) environmental transportation and distribution of MP and (3) the effects of MP on biota, including the additives and sorption-desorption of MP in both terrestrial ecosystem and aquatic ecosystems were summarized. Based on the reviewed publications, we propose considerations for addressing the insufficiencies of analytical methods, distribution and biological effects of MP in ecosystems so we can adequately safeguard global ecosystems.
The accumulation of plastic debris and herbicide residues has become a huge challenge and poses many potential risks to environmental health and soil quality. In the present study, we investigated the transport of glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA) via earthworms in the presence of different concentrations of light density polyethylene microplastics in the litter layer during a 14-day mesocosm experiment. The results showed earthworm gallery weight was negatively affected by the combination of glyphosate and microplastics. Glyphosate and AMPA concentrated in the first centimetre of the top soil layer and the downward transport of glyphosate and AMPA was only detected in the earthworm burrows, ranging from 0.04 to 4.25 μg g⁻¹ for glyphosate and from 0.01 (less than limit of detection) to 0.76 μg g⁻¹ for AMPA. The transport rate of glyphosate (including AMPA) from the litter layer into earthworm burrows ranged from 6.6 ± 4.6% to 18.3 ± 2.4%, depending on synergetic effects of microplastics and glyphosate application. The findings imply that earthworm activities strongly influence pollutant movement into the soil, which potentially affects soil ecosystems. Further studies focused on the fate of pollutants in the microenvironment of earthworm burrows are needed. Glyphosate was mainly transported into deeper soil layers via earthworm galleries which were influenced by synergetic effects of microplastics and glyphosate application.
Microplastics are emerging contaminants of increasing concern. Despite the occurrence of microplastics in farmland soils, the knowledge on microplastics in rice-fish co-culture ecosystems is limited. In this study, we investigated the distribution of microplastics in three rice-fish culture stations in Shanghai. During non-rice and rice-planting periods, microplastics in water, soils and aquatic animals (eel, loach and crayfish) were systematically assayed using methods of NaCl density extraction, H2O2 digestion and micro-fourier transform infrared spectroscopy. Results showed that average microplastic abundances were 0.4±0.1 items L-1, 10.3±2.2 items kg-1, 1.7±0.5 items individual-1 in water, soils and aquatic animal samples, respectively. We found an increasing trend in microplastic abundances in water, soil and animal samples from non-rice period to rice-planting period. Almost all of microplastics were found in digestive tracts of animals. Major microplastics were small (<1 mm) polyethylene and polypropylene fibers, with color of white and translucent. Size, shape, color and polymer type distributions of microplastics were similarly found in environmental and animal samples. Moreover, microplastic abundances in aquatic animals correlated to abundance in farmland soils. This study, for the first time, reveals the occurrence and characteristics of microplastic pollution in rice-fish culture ecosystem which suggests the potential ecological risks of microplastics in the agroecosystem.
Misuse/over use of antibiotics increases the threats to human health since this is a main reason behind evolution of antibiotic resistant bacterial pathogens. However, metals such as mercury, lead, zinc, copper and cadmium are accumulating to critical concentration in the environment and triggering co-selection of antibiotic resistance in bacteria. The co-selection of metal driven antibiotic resistance in bacteria is achieved through co-resistance or cross resistance. Metal driven antibiotic resistant determinants evolved in bacteria and present on same mobile genetic elements are horizontally transferred to distantly related bacterial human pathogens. Additionally, in marine environment persistent pollutants like microplastics is recognized as a vector for the proliferation of metal/antibiotics and human pathogens. Recently published research confirmed that horizontal gene transfer between phylogenetically distinct microbes present on microplastics is much faster than free living microbes. Therefore, microplastics act as an emerging hotspot for metal driven co-selection of multidrug resistant human pathogens and pose serious threat to humans which do recreational activities in marine environment and ingest marine derived foods. Therefore, marine environment co-polluted with metal, antibiotics, human pathogens and microplastics pose an emerging health threat globally.